Psora gresinonis B. de Lesd.

Bull. Soc. Bot. France, 77: 614, 1930.
Synonyms: Lecidea gresinonis (B. de Lesd.) Zahlbr.
Distribution: N - Lig (Roux & al. 2025a). C - Sar. S - Cal (Puntillo 1996).
Description: Thallus squamulose, the squamules olivaceous brown to dark brown, epruinose, 0.5-5.5 mm wide, up to 0.35 mm thick, rounded, adnate, scattered to contiguous, with thin, grey- to white- edged margins, more or less lobed, the upper surface smooth, not divided by small fissures, the lower surface black, attached by colourless to brownish rhizohyphae and a few rhizines. Upper cortex overlain by an epinecral layer, colourless or brownish in upper part, 50–70 μm thick, paraplectenchymatous, with large crystals insoluble in K and in N; algal layer continuous; medulla white, in upper part, brownish in lower part, lax, arachnoid, 60–100 μm thick, inspersed with crystals; lower cortex prosoplectenchymatous, 8–15 μm thick, whithout crystals. Apothecia biatorine, sessile, 0.5-1 mm across, usually clustered, with a black, convex disc and a thin, mostly indistinct and soon excluded proper margin. Proper exciple thin, of anticlinally arranged hyphae resembling paraphyses; epithecium reddish brown, containing orange crystals dissolving in K, K+ purple, N-; hymenium colourless, 80–95 μm high, hemiamyloid; paraphyses coherent, simple or sparingly branched, rarely anastomosing, 1.5-2 μm thick at mid-level, the apical cell slightly swollen; subhymenium colourless, 80–95 μm high, I-; hypothecium colourless, 40–160 μm high, with crystals of calcium oxalates, soluble in N, and insoluble in K. Asci 8-spored, elongate-clavate, with a thin, outer amyloid layer and a thickened tholus penetrated by a tube, the sides of which stain I/KI+ deep blue, without an ocular chamber, Porpidia-type. Ascospores 1-celled, hyaline, ellipsoid, thin-walled, (8.5-)11-15(-16) x (4.5-)6-7(-8) µm. Photobiont chlorococcoid. Spot tests: cortex K-, C-, KC-, P-, UV-; medulla K+ yellow turning red (needle-like red brystals), P+ yellow-orange. Chemistry: cortex without lichen substances, medulla with norstictic acid; epithecium with anthraquinones, mainly parietin.
Note: on soil, in fissures of lime-free siliceous rocks, with optimum in dry grasslands at relatively low elevations, with a mainly Mediterranean and Tyrrhenian range in Italy. For further details and an extended description see Roux & al. (2025a).
Growth form: Squamulose
Substrata: soil, terricolous mosses, and plant debris
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly sexual

Commonnes-rarity: (info)

Alpine belt: absent
Subalpine belt: absent
Oromediterranean belt: absent
Montane belt: absent
Submediterranean belt: extremely rare
Padanian area: absent
Humid submediterranean belt: very rare
Humid mediterranean belt: very rare
Dry mediterranean belt: absent

pH of the substrata:

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Solar irradiation:

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Aridity:

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Eutrophication:

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Poleotolerance:

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Altitudinal distribution:

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Predictive model
Herbarium samples
INDEX FUNGORUM GBIF


P.L. Nimis CC BY-SA 04
TSB 10088



P.L. Nimis; Owner: Department of Life Sciences, University of Trieste
Herbarium: TSB (10088)
2001/11/29


Source: https://nhm2.uio.no/typephotos/lichens/arkiv/O-L-000133d.jpg
ITALY, LIGURIA: Liguria occid.: Spotorno. In argillosis loco La Torre, 1949.05.29, Sbarbaro, C. - ISOTYPE


Source: Evankow, A.M., Yin, A., Zulfiqar, R. et al. Psora mediterranea (Lecanorales, Psoraceae), a new lichen species from Europe, including a new concept for P. himalayana and a revised key to the European species. Mycol Progress 24, 26 (2025). https://doi.org/10.1007/s11557-025-02045-8 - CC BY 4.0
Italy, isotype: O-L-133, Photo: E. Timdal